This invention relates to a hydraulic generator drive system. More specifically, this invention relates to a robust control system for a hydraulic generator drive.
Hydraulic generator drive systems are used in the operation of heavy machinery such as pavers, agricultural tractors, utility trucks, fire trucks, cranes and similar machines. A hydraulic generator drive system typically is powered by an internal combustion engine that provides a mechanical input to a hydraulic pump. The hydraulic pump is hydraulically connected to a hydraulic motor to provide power to the generator at constant speed. There are a variety of control systems used to operate the conventional hydraulic generator drive system. In general, each is based upon the identical concept of controlling the speed of the generator simultaneously with controlling the voltage of the generator using two different control systems. Each of these systems has its own individual problems including generally high cost and instability in the system due to the separate control systems not working properly in unison.
FIGS. 1-4 represent prior art control systems used to operate hydraulic generator drive systems. FIG. 1 shows a traditional control that incorporates a load sensing control for the output of the pump and a standard automatic voltage regulator control (AVR) for the output of the generator. The load sense control on the pump tries to maintain a constant margin across the “fixed flow control orifice” which maintains a constant flow through this orifice. One of the problems with this control system is that the pump may maintain a constant flow across the orifice; however, there is leakage in the hydraulic motor and as the load increases there is more leakage across the motor. As the load increases the speed of the generator decays even if the flow from the pump remains constant. The problem with this control system is that there are two separate closed loop control systems that can affect each other negatively and causes instability in the whole system.
FIG. 2 shows a second traditional control system that incorporates a flow valve and a standard AVR for the output of the generator. The load sense control of the valve tries to maintain a constant margin across an orifice which maintains a constant flow through this orifice. One of the problems with this control system is that the valve may maintain a constant flow across the flow; however, there is leakage in the hydraulic motor and as the load is increased there is more leakage across the motor. Again, the result is as the load increases the speed of the generator decays even if the flow from the valve remains constant. The problem with this control system is that there are two separate closed loop control systems that can affect each other negatively and causes instability in the whole system.
FIG. 3 shows a third traditional control system. This control system also utilizes a flow control valve and incorporates a closed loop electronic speed control that controls the flow out of the valve. Additionally, the system has a standard AVR for the output of the generator. The problem with this control system is that there are two separate closed loop control systems that can affect each other negatively and causes instability in the system.
FIG. 4 shows a fourth traditional control system that uses an EDC pump control. This control system incorporates a closed loop electronic speed control which controls the flow out of the pump and a standard AVR for the output of the generator. Several problems are presented with this design including that flow control pumps are more expensive than pressure control pumps. Additionally, as with the other circuits, two separate closed loop control systems are presented that affect each other negatively that causes instability within the entire system.
A final prior art control system is shown in FIG. 5 that utilizes a throttle on the internal combustion engine and a fixed displacement pump. In this prior art system a closed loop electronic speed control controls the throttle of the internal combustion engine while a standard AVR is used to control the output of the generator. Again, because two separate closed loop control systems are presented, instability problems occur in the system. Additionally, while this system has been proven to operate satisfactorily when the engine is dedicated to running the generator, oftentimes systems need the engine to run more than just the generator. As a result, the versatility of this system is limited.
Therefore, a principal object of the present invention is to provide a hydraulic generator drive system that utilizes a control system having a single control system.
Another object of the present invention is to improve stability of a hydraulic generator drive system.
These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.